1. Field of the Invention
The present invention relates to a cooling medium path structure of a root portion of a gas turbine blade.
2. Description of the Related Art
The structure of a conventional cooling medium path of the above type will be described with reference to FIGS. 11 through 13. In the outer periphery of a turbine disk 2 there are formed in the axial direction a plurality of inverted Christmas tree-shaped blade grooves 7 at equal intervals in the circumferential direction so as to correspond in number to turbine blades 1 fitted in the respective stages.
At the same time, in a root portion of the turbine blade 1, there are provided inverted Christmas tree-shaped portions 8 which can be assembled into the above-mentioned inverted Christmas tree-shaped grooves 7 with a very small gap therebetween.
Each turbine blade 1 is inserted to be assembled into the respective groove of the turbine disk 2 one by one in the axial direction so that during the operation of the turbine, the turbine disk 2 bears the centrifugal force and the vibrating force through a teeth engagement of the inverted Christmas tree-shaped groove 7 and the same-shaped portion 8.
Further,once the turbine blade 1 is so assembled into the turbine disk 2, then it is so designed that the shapes of the blade groove 7 of the turbine disk 2 and the mating portion 8 at the root portion of the turbine blade 1 secure a cooling medium path 9 for allowing a cooling medium flow in the bottom portion of the blade 1.
The cooling medium (usually a compressed air) for cooling the turbine blades 1 passes through radial directional holes 10, which are the same in number as the blades of the respective stage and which are formed on the side of entrance of the turbine disk 2 and is introduced into a space 14 surrounded by sealing blocks 12 and 13.
After that, the cooling medium is introduced into the cooling medium path 9 formed at the bottom portion of the inverted Christmas tree-shaped portion 8, enters a passage (not shown) formed at the root portion of the turbine blade 1 and flows into the interior of the blade l thereby cooling the whole of the blade. The cooling medium having thus cooled the blade 1 is discharged into a subsequent gas path.
In the mentioned course of a series of flows of the cooling medium, the cooling medium path 9, which is formed between the blade groove 7 and the portion 8 formed at the root portion of the turbine blade 1, defines the space 14 surrounded by the sealing blocks 12 and 13 at the entrance of the disk 2 located on the upstream side of the above-mentioned gas path while it is defined by a sealing piece 15 and a fixing piece 16 at the exit of the disk 2 located on the downstream side of the gas path.
Normally, the upstream side sealing block 12 and the downstream side sealing piece 15 are provided for every two blades 1 and the upstream side sealing block 13 and the downstream side fixing piece 16 are provided for each blade 1 and all of these parts are assembled at their proper positions, respectively.
Accordingly, in order to assemble these parts and the other parts associated therewith, it becomes necessary to provide suitable spaces for receiving them in position so that it is unavoidable that gaps will be left unoccupied in some places even after assembly.
In FIGS. 11 and 13, reference numeral 17 designates a sealing plate for covering a small gap formed between the inverted Christmas tree-shaped groove 7 and the mating portion 8 of the same shape and since this plate 17 is usually used for each of the blades 1, there is left a space required for assembling it.
As described above, it has been usual with the conventional cooling medium path structure that there exist, in the structure, various kinds of spaces or gaps left intentionally or resultantly for the convenience of designing, manufacturing and assembling the entire structure so that even when cooling air or the like as a cooling medium is supplied through the holes drilled in the disk 2, it leaks from the gap around the cooling medium path or the sealing plate so that the cooling air or the like cannot be collected but is discharged into the gas path. Consequently, there has been a problem of recovering and using the cooling medium heated to a high temperature after being used for cooling and the resultant thermal efficiency loss has been unavoidable.